The presence of impurities in pure cobalt metal powder may adversely affect the properties of items manufactured from the cobalt metal powder. Similarly, the presence of impurities in the cobalt-containing source materials from which the pure cobalt metal powder is obtained may adversely affect the powder manufacturing process. For example, the presence of impurities in the pure cobalt metal powder may decrease the strength and increase the porosity of articles made from the powder. Similarly, the presence of heavy metals, such as cadmium, in the cobalt-containing source materials may lead to a release of toxins harmful to those who handle the materials as well as to the environment. A "heavy metal" is defined as a metal having a specific gravity of 5.0 or greater, or whose density is at least five times that of water.
It would be advantageous to remove such potentially harmful impurities from the cobalt-containing source materials during the cobalt powder manufacturing process.
U.S. Pat. No. 4,612,039 to Scheithauer et al., the disclosure of which is hereby incorporated by reference, describes a method for producing pure cobalt metal powder in which a cobalt-containing source material is reduced to an intermediate cobalt metal, which is then oxidized in an ammoniacal ammonium halide solution in the presence of a catalyst. The product of the oxidation reaction is a solution containing hexammine cobalt (III) ions, to which a halide salt is added to form a hexammine cobalt (III) halide precipitate. The precipitate is dissolved in water, and the resulting solution is rendered basic and then heated to form an insoluble cobalt oxide-containing material. This material is then reduced to form pure cobalt metal powder.